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Heat Budget of Earth
A heat budget is a precise balance between the heat that the earth radiates away from the sun and the heat that it collects from the sun (Insolation or terrestrial radiation).
Earth would be getting either too warm or too cold if the balance between incoming and existing heat were off. These variables are properly balanced, which results in the perfect temperature of the earth. The equilibrium between insolation (short waves) and terrestrial radiation is known as the Earth’s Heat Budget (long waves).
Read More: Heat Transfer Methods
Heat Budget of Earth Atmosphere
Depending on its location, the Earth’s surface receives different amounts of solar radiation, with some areas receiving more than others. Between 40°N and 40°S, there is a surplus of net radiation balance, whereas there is a deficit in the areas close to the poles.
The poles receive a redistribution of the extra heat energy from the tropics. This balance is absolutely essential because it prevents the tropics from becoming extremely hot from the buildup of excess heat and prevents locations at high altitudes from becoming permanently frozen from a lack of radiation.
Read More: Isotherms
Heat Budget of Earth in Detail
The concept of a heat budget is related to how much solar heat energy is collected and utilised both on the surface of the earth and in the atmosphere. The average temperature of the Earth overall does not change despite the continuous supply of sun rays. This is only possible if the Earth’s system sends an equal quantity of energy back into space. There is a balance or equilibrium between incoming solar radiation & outgoing terrestrial radiation. This balance is known as the Heat Budget of Earth.
Let’s consider that the insolation received at the top of the atmosphere is 100 per cent. While passing through the atmosphere, some amount of energy is reflected, scattered, and absorbed. Only the remaining part reaches the Earth’s surface. Even before they reach the surface of the Earth, around 35 units are reflected back to space. The detailed break-up of this reflected radiation is as under:
- From the top of clouds, Reflected Radiations – 27 units
- By ice fields on earth, Reflected Radiations – 02 units
- Reflected by the atmosphere – 06 units
- Total – 35 units
Albedo of the Earth
The reflected amount of radiation has referred to the albedo of the Earth. Thus, this 35 per cent of radiation neither heats the atmosphere nor the Earth’s surface. The remaining 65 units are absorbed as:
- Absorbed by the atmosphere – 14 units
- Absorbed by the earth – 51 units (Scattered + direct radiation)
- Total – 65 units
Gas molecules and dust particles cause scattering. This occurs in all directions, with part of it moving towards the planet and some toward space. Overall, the earth receives 51 units of radiation, which radiates back in the form of terrestrial radiation. The details about this reflected radiation are as described in the following:
- Radiated to space directly – 17 units
- Radiated to the atmosphere – 34 units
The details of 34 units of radiation absorbed by the atmosphere from terrestrial radiation are:
- Absorbed directly – 06 units
- Absorbed through convection and turbulence – 09 units
- Absorbed through Latent heat of condensation5 – 19 units; (Latent heat refers to the energy released or absorbed by a body)
- Total – 34 units
The total units absorbed by the atmosphere are 48 (14 units of insolation + 34 units of Terrestrial radiation). These are radiated back into space. Thus, the total radiation returning from the earth and the atmosphere respectively are:
- Radiated back by earth – 17 units
- Radiated back by the atmosphere – 48 units
- Total – 65 units
These returning 65 units balance the total of 65 units received from the sun. This account of incoming and outgoing radiation always maintains the balance of heat on the earth’s surface. This is known as the heat budget of earth or heat balance of the earth.
Read More: Temperature Inversion
Heat Budget of Earth Diagram
The world maintains a constant temperature through this exchange of heat, and this phenomenon is known as the earth’s heat budget. Here is the diagram of the Heat Budget.
Read More: Heat Zones of Earth
Latitudinal Heat Balance
Although the whole earth maintains a balance between the incoming and the outgoing radiation of the earth, this is not true when we look at different latitudes. At the latitudinal level, the heat budget is not zero. As discussed earlier, the insolation obtained is directly related to latitudes. One part of the world has a surplus radiation balance, and the other part is lacking. There is a surplus of radiation balance between 40 degrees N&S and the regions near the poles are in short supply. This, in theory, should mean that the tropics should gradually warm up and that the Arctic and Antarctic become even cooler. But that is not the case. The excess heat energy from the tropics is redistributed towards the poles by ocean currents, wind flow, air circulation etc.
As a result, the tropics neither heat up continuously due to excessive heat accumulation, nor the polar latitudes are permanently under snow due to extreme shortages. According to some estimates, about 75 per cent of the heat is transferred through atmospheric circulation and the remaining 25 per cent is transferred by oceanic circulations. Winds and currents in the oceans are produced due to thermal imbalances.
Read More: List of Major Local Winds
Heat Budget of Earth UPSC
The sun is the most powerful heat generator. And the primary cause of all climatic traits is the varied amounts of heat that different parts of the globe receive from the sun. In order to comprehend various climatic elements like wind systems, pressure systems, precipitation, etc., it is vital to understand the patterns of temperature distribution in different seasons. A crucial component of your UPSC preparation is geography. Both the UPSC Prelims and Mains General Studies Paper I include it. You may study everything about Heat Budget for the IAS Exam in this post.